Automatic shotgun choke



Aug. 19, 1958 I L. A. TWIGG AUTOMATIC SHOTGUN CHOKE 2 Sheets-Sheet 1Filed on. a, 1955 LESTER A. TWIGG INVENTOR AGENT L. A. TWIGG 2Sheets-Sheet 2 9 A H N o I- u INVENTOR LESTER A. TW/GG AGENT Aug. 19,1958 AUTOMATIC SHOTGUN CHOKE Filed 001;. 5, 1955 R on mm mm R 9 mm v 6ttes atent 2,847,788 Patented Aug. 19, 1958 AUTOMATIC SHOTGUN CHOKELester A. Twigg, Bethesda, Md.

Substitute for abandoned application Serial No. 321,810, November 21,1952. This application Gctober 3, 1955, Serial No. 538,205

Claims. (Cl. 42-79) The present invention relates to adjustable shotgunchokes. More particularly, it relates to a choke which is attachable tothe muzzle of a cylinder bore gun, so that the effective bore diametermay be altered automatically by the passage of a shot load therethrough.

This application is substituted for application Serial Number 321,819,filed November 21, 1952, now abancloned.

A typical example of the application of semi-automatic chokes forshotguns is found in field bird shooting, and in shooting doubles at theclay pigeon trap. Usually the choke is set at cylinder (no choke) forthe first shot and at full choke or choke for the second shot. As it isprobable that the first bird or clay target would be near to the shooterat the moment of the first shot, an open shot pattern first would bemost appropriate. The shot is then dispersed over a greater area, andthereby increases the probability of securing a hit. If, however, theshooter misses at close range, continued use of an open shot patternwould be undesirable. As will be understood, an individual shot does notpossess the lethality at extended range which it possesses at closerange. Therefore, a more concentrated shot pattern is required forcertain results. In addition, at extended ranges, the shooter has moretime to aim his'fire precisely, and therefore a broad pattern is notrequired to insure hits.

Prior adjustable chokes of the manual type are unsatisfactory for rapidfire shooting simply because little time is available to manipulate thechoke. Prior chokes of the automatic type have not proved successful forthe reason that they are unreliable in operation. Frequently, automaticchoke devices have been discarded in favor of a double-barrelled shotgunhaving one barrel cylinder bored and the other barrel choke bored. Sucha gun dependably affords the appropriate shot pattern for the usualsituation in which a hunter may find himself. However, double-barrelledguns are considerably more expensive than a single barrel type, and donot possess the desirable feature of providing a wide variety of shotpatterns.

Accordingly, it is an object of the present invention to provide themeans for obtaining varied shot patterns with two successive loads in asingle barrel gun.

Another object of the present invention is the provision of a shotgunchoke variable from a first degree of choke to a fuller, or moreconstricted choke, by the passage of the first shot load therethrough.

Still another object or the present invention is to provide a two-shotshotgun choke which possesses two preset choke conditions and which issimply and quickly reset to the initial choke condition after the secondshot is fired.

Gther objects and advantages will become evident as an understanding ofthe invention is gained through consideration of the following detaileddescriptions and the accompanying drawings.

In the drawings:

Fig. 1 is a perspective view of the choke of the present invention.

Fig. 2 is a perspective view of the component parts of the invention.

Fig. 3 is an elevation view of the invention, and

Fig. 4 is an axial section taken along the line 4-4 of Fig. 3.

Referring now to the drawings, and particularly to Figs. 1 and 2thereof, where the invention is seen assembled and broken down into itscomponent parts.

In their order of assembly, the components of the automatic choke 10 ofthe present invention include, a choke tube 11 and a compression tube12, into which the forward portion of choke tube 11 is slidinglyinserted. The choke tube 11 and compression tube 12 are then insertedinto an adjusting cylinder 13, which, as is more fully explainedhereinafter, limits the sliding motion of the compression tube 12, afterthe first shot is fired. The choke tube 11, compression tube 12 andadjusting cylinder 13 are secured in operative relationship by aninternally threaded retaining tube 14, the threads of which engagemating threads on both the choke tube 11 and adjusting cylinder 13.Finally, a grip ring 15 is secured to the forward end of compressiontube 12, to aid manual adjustment of compression tube 12. The choke 10is then in fully assembled relationship as it appears in Fig. 1.

As the invention will be better understood by comprehension of its modeof operation, the function of its elements will first be brieflyconsidered before commencing their detailed description.

The choke tube 11 functions, as is conventional, in prior adjustablechokes, to diminish the bore of the gun to which the choke I0 isattached. Accordingly, the bore of the choke tube is variable fromcylinder to full choke by compression of its forward expandable portion16. The compression is accomplished by a forward sliding movement of thecompression tube 12, which is internally tapered from front to rear. Asfull choke may not be desired, the adjusting cylinder 13,is adapted toarrest the forward sliding movement of the compression tube 12 in anyposition intermediate between cylinder bore and full choke.

In Figs. 3 and 4, the details of the invention may be seen. The rearinternal diameter of choke tube 11 is chosen to provide a snug fit withthe outside diameter of the barrel of the gun (not shown), to which thechoke is to be attached by threads 21 or other suitable means. Themuzzle of the gun abuts against shoulders 22 which are formed byreducing the bore of the choke tube 11 to the diameter corresponding tothe bore of the gun.

The forward end portion of the choke tube 11 is provided with aplurality of axially extending slots 23, spaced about the circumferenceof the tube. The slots thereby provide a plurality of fingers 24, Whichconstitute the variable diameter portion of the choke tube 11. Thematerial of which the tube 11 is constructed preferably possessessufiicient resilience so that the fingers 24 may be compressed inwardlywithout acquiring a permanent inward set.

The exterior of the forward portion 16 of the choke tube 11 is finishedwith a front to rear inward taper. Similarly, tapered internal surfacesof the compression tube 12 are provided so that a compression of thefingers 16 will be provided upon the forward sliding movement of thecompression tube 12. Thus, commencing at 25, the external diameter ofchoke tube 11 tapers to a minimum external diameter at 26. At 27, theexternal diameter is enlarged to provide Walls of adequate strength inthe region of the gun muzzle and to provide a rear stop to arrestbackward movement of'the compression tube 12.

The Compression tube 12 is internally bored to mate closely with theexterior of choke tube 11 and is pro- 'vided with an interior tapercorresponding to the ex- 'terior taper of the choke tube 11. Theinternal diam- 'eter of of compression tube 12 is greatest at itsforward end and tapers to a minimum approximately at 26. The exterior ofcompression tube 12 is finished as a smooth cylinder.

The compression tube 12 extends beyond the forward end of choke tube 11and thereby provides, as is explained hereinafter, the forces forcausing its forward sliding movement. A flange 28 is turned on the rearend of compression tube 12 for the purpose of engaging a shoulder 29turned internally on adjusting cylinder 13, cylinder 13 being bored toslidingly receive tube 12. Holes 37 may be provided in the forwardportion of compression tube 12 to increase shot load drag forces and toreduce muzzle blast.

As will now be understood, the degree of choke depends upon the distancewhich the compression tube is allowed to travel in the forwarddirection. Therefore, by arranging the adjusting cylinder 13 to permit avariation of the distance separating shoulders 27 and 29, any desireddegree of choke from cylinder to full choke may be obtained.

The retaining cylinder 14 and adjusting cylinder 13 are threadedtogether by threads 30, so that the adjusting cylinder 13 may beretracted into retaining cylinder 14. A flange 31 is formed at the rearend of adjusting cylinder 14 so that cylinder 14 may be firmly securedto choke tube 11 with adequate clearance preserved to permit theretraction of cylinder 13 within cylinder 14. Cylinder 14 may be securedto choke tube 11 by threads 32, or, if desired, by a tight press fit,since tube 11 and cylinder 14 are not required to move relative to eachother. Grip ring 15 is secured to the forward end of choke tube 12 byset screws 33.

Referring particularly to Fig. 3, the compression tube 12, and adjustingcylinder 13 are graduated to indicate the degree of choke for which thedevice is set. An index pointer 35, labelled for 1st shot and 2nd shotsettings, indicates by alignment with one of the graduations 36 theprecise degree of choke obtainable for the first and second shots.

The graduations conform to conventional definitions of the variousdegrees of choke. Cylinder, of course, indicates the open choke positionin which the choke bore corresponds with the gun bore, assuming the gunto be cylinder bored. In the case of a 12 gauge gun, a cylinder bore gunhas a diameter of approximately .729 inch, and therefore the bore of thechoke corresponds to this dimension when adjusted to cylinder. Again,conventionally, the full choke diameter is defined as .689 inch for a 12gauge gun. Therefore, the taper of the choke tube 11 and compressiontube 12 must be such to reduce the bore of the choke by .040 inch whenthecompression tube is in its extended position. In one 12 gaugeembodiment of the invention, .75 inch has been found to be satisfactoryfor the length of the taper, the rate of taper therefore being .0266inch inward per inch of axial length.

In use the device functions as follows:

Adjusting cylinder 13 is rotated until the graduation indicating thedesired degree of choke is aligned with the 2nd shot position of index35. Compression tube 12 is then adjusted by sliding the same axiallyuntil the graduation indicating the desired degree of choke is alignedwith the 1st shot position of index 35. Any degree of choke may beselected for the second shot and any degree of choke intermediatebetween that selected for the second shot and cylinder may be selectedfor the first shot. The selections illustrated in Fig. 3 are choke forthe first shot and choke for the second.

Upon firing the first shot, as the load passes beyond the forward end ofchoke tube 11, invariably several of the shot or pieces of waddingcontact the forward wall of compression tube 12. Frictional drag forcesare thus created which cause the compression tube to slide forward untilflange 28 engages shoulder 29. This position provides the degree ofchoke preselected for the second shot. The choke is thereforeautomatically prepared for the second shot which may be firedimmediately after the first shot. After firing the second shot, it isonly necessary manually to retract compression tube 12 to the desiredfirst shot choke condition. The cycle can then be repeated.

The features of the present invention which render its operationreliable, insure its long life, and simplify its construction includethe elimination of spring loaded devices and devices operating by gaspressure. The operating forces of the present choke arise purely as aresult of shot load drag. Furthermore, the force required for operatingthe choke is not large, since, by reason of the compression tubesextension beyond the end of the choke tube, compression of the choketube is not required to be accomplished against the load pressure of thebarrel. That is, with the load occupying the forward portion of thecompression tube, the choke is effectively relieved of load pressurewhen the choke setting operation occurs. Gas pressure exists in thechoke tube, however gas may leak through the slots 23 of the choke tubeto equalize the pressure on both surfaces of the fingers 24. Thus onlymoderate drag force is required to move the compression tube forward tothe second shot position.

Many modifications and variations are possible in the light of the aboveteachings. It is therefore to be understood that within the scope of theappended claims the invention may be practiced otherwise than asspecifically described.

What is claimed is:

1. An automatic choke for firearms comprising, an expansible choke tubeincluding a plurality of resilient fingers normally flexed outwardly toprovide an open shot pattern, means for securing said choke tube to themuzzle of a gun, a second tube movably receiving said choke tube, saidsecond tube projecting beyond the open end of said choke tube and beingadapted for forward sliding motion relative to said choke tube, means onsaid second tube for flexing said fingers inwardly to provide a closedshot pattern upon movement of said second tube with respect to saidchoke tube, a third tube enclosing the rear portion of said second tubeand including means for arresting forward movement of said second tube,and a fourth tube secured to said choke tube and adjustably receivingthe rear portion of said third tube whereby the forward motion of saidsecond tube may be arrested at intermediate choke stops.

2. A choke as claimed in claim 1 wherein said means for flexing saidfingers inwardly comprises a tapered surface provided internally of saidsecond tube,.said tapered internal surface bearing on the externalsurface of said choke tube.

3. A choke as claimed in claim 2 with additionally, means on said choketube for indicating the longitudinal position of said second tuberelative to said choke tube.

4-. A choke for firearms comprising, a first tube having a slottedforward end portion to provide a plurality of resilient fingers, saidfingers normally being flexed outwardly to provide an easy shot pattern,means at the rear end portion of said first tube for securing said firsttube to the muzzle of a firearm, a second tube slidingly enclosing saidfirst tube and extending beyond the forward end thereof, said secondtube including an outwardly directed shoulder at the rear thereof andhaving a tapered internal surface bearing on said slotted forward endportion of said first tube to flex said fingers inwardly upon slidingmovement of said second tube with respect to said first tube, a thirdtube secured to said first tube so as to enclose the rear portion ofsaid second tube and including an inwardly directed shoulder forengaging said shoulder on said second tube to limit the sliding movementof said second tube with respect to said first tube, and means on saidfirst tube for indicating the longitudinal position of said second tubewith respect to said first tube.

5. A choke for firearms comprising, a choke tube adapted to be securedto the muzzle of a firearm and having a slotted forward end portion forforming a plurality of resilient fingers normally flexed outwardly toprovide an open shot pattern, said plurality of fingers each beingprovided with a tapered external surface, a compression tube slidinglyenclosing said slotted forward portion of said choke tube and extendingbeyond the forward end thereof, said compression tube being providedwith a tapered internal surface for hearing on said tapered externalsurfaces of said fingers to compress said fingers inwardly, a shoulderformed on said compression tube, an adjusting cylinder adjustablysecured to said choke tube and receiving said choke tube and compressiontube, a shoulder on said adjusting cylinder for engaging said shoulderon said compression tube, means including graduations along saidcompression tube for indicating in terms of degree of choke thelongitudinal position of said compression tube with respect to saidchoke tube, and means including graduations along said adjusting tubefor indicating in terms of degree of choke the longitudinal position ofsaid adjusting tube with respect to said choke tube, whereby the dragforces created by the abrasion of shot against the forward Walls of saidcompression tube urge said compression tube forward and said shouldersinto engagement thereby altering the bore of said choke tube in theamount indicated by said last a named means.

References Cited in the file of this patent UNITED STATES PATENTS

